Hydrogen Lyman-alpha Line Research Articles

Solar Extreme and Far Ultraviolet Radiation Modeling for Aeronomic Calculations

Modeling the upper atmosphere and ionospheres on the basis of a mathematical description of physical processes requires knowledge of ultraviolet radiation fluxes from the Sun as an integral part of the model. Aeronomic models of variations in the radiation flux in the region of extreme (EUV) and far (FUV) radiation, based mainly on the data of the last TIMED mission measurements of the solar spectrum, are proposed. The EUVT model describes variations in the 5–105 nm spectral region, which are responsible for the ionization of the main components of the earth’s atmosphere. The FUVT model describes the flux changes in the 115–242 nm region, which determines heating of the upper atmosphere and the dissociation of molecular oxygen. Both models use the intensity of the hydrogen Lyman-alpha line as an input parameter, which can currently be considered as one of the main indices of solar activity and can be measured with relatively simpler photometers. A comparison of the results of model calculations with observations shows that the model error does not exceed 1–2% for the FUVT model, and 5.5% for EUVT, which is sufficient for calculating the parameters of the ionosphere and thermosphere.

Catalog and Statistical Examinations of Lyα Solar Flares from GOES/EUVS-E Measurements

Abstract The Lyman-alpha (Lyα) line of neutral hydrogen at 121.6 nm is by far the brightest emission line in the vacuum ultraviolet spectral range of the Sun. The emission at this line could be a major energy input to the upper layers of the Earth’s atmosphere, strongly impacting the geospace environment. The Geostationary Operational Environmental Satellite (GOES) series, starting with GOES-13, began to carry a multichannel Extreme UltraViolet Sensor (EUVS) with one channel (E-channel) targeting the Lyα line. In the present work, we produce a Lyα flare catalog from the GOES-15/EUVS-E data between 2010 April 8 and 2016 June 6 with an automatic flare detection algorithm. This algorithm is designed to search events at various scales and find their real start and end times. Based on the obtained flare list, statistics on the temporal behavior such as the duration, rise, and decay times, and the event asymmetries of Lyα flares is presented. On average (defined by the median of the distributions), the duration, rise and decay times of the flares were estimated to be 20.8 minutes, 5.6 minutes, and 14.2 minutes, respectively. We also discuss the frequency distributions of the peak flux and the fluence of Lyα flares, both of which reveal power-law behaviors with power-law indices of 2.71 ± 0.06 and 2.42 ± 0.06, respectively, implying that more flares are accumulated at small scales and these small-scale events play an important role in explaining the violent solar energy release.

Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission

As the Lyman-alpha (Lyupalpha ) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Lyupalpha of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ≈8500 flares greater than B1 class to determine the contribution that they make to changes in the solar EUV irradiance. Using the peak of the 1 – 8 Å X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Lyupalpha emission by the EUV Sensor on the Geostationary Operational Environmental Satellite 15 (GOES-15) were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1 – 0.3% enhancement to the solar Lyupalpha irradiance on average. For comparison, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1 – 4% increase in Lyupalpha emission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Lyupalpha at the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Lyupalpha of 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.

Specific Features of Radiation Transfer in the Hydrogen Lyman-alpha Line and Their Possible Relationship with Changes in the Electron Concentration in the Ionospheric D Region

The effect of neutral atmospheric parameters on the radiation transfer in the Lyman-alpha line and the electron concentration in the ionospheric D region is studied for various seasons and nitric oxide (NО) concentrations. The radiation transfer was calculated with a modified radiation transfer model that allows multiscattering radiation effects. The atomic hydrogen and molecular oxygen profiles affecting Lyman-alpha radiation propagation were given with the MSIS-00 model. It is shown the radiation fluxes in the Lyman-alpha line and the electron concentration in the D region can be markedly affected upon sudden stratospheric warming and by the influence of planetary waves on the mesosphere. The changes in radiation fluxes in the Lyman-alpha line under unstable atmospheric conditions in the winter and the possible NО variations qualitatively explain the phenomenon of the winter anomaly.

Vacuum ultraviolet quarter wave plates based on SnTe/Al bilayer: Design, fabrication, optical and ellipsometric characterization

Vacuum ultraviolet and extreme ultraviolet polarized light plays a significant role in many applications from materials science and solar physics investigations to optical components development. In this paper, we study the optical performances and the quarter wave retarder properties of aluminum coating capped with SnTe/Al thin film. The measurements have been performed by using a reflectometer properly improved for ellipsometric characterizations. The specimen has been fully characterized at hydrogen Lyman–alpha line (121.6 nm) by deriving the reflectance and the ellipsometric parameters, i.e. the ratio r and the phase difference δ. We found that the SnTe/Al bilayer behaves as phase retarder, although the performances differ from the ideal case. In fact, the polarimetric analysis combined with the optical test at different wavelengths allowed to identify carbon contamination on the top layer and a mild oxidation of the aluminum coating that affect the optical throughput.

Puzzling Lyman-alpha line profiles in green pea galaxies

Context. The Lyman-alpha (Lyα) line of hydrogen is of prime importance for detecting galaxies at high redshift. For a correct data interpretation, numerical radiative transfer models are necessary due to Lyα resonant scattering off neutral hydrogen atoms. Aims. Recent observations have discovered an escape of ionizing Lyman-continuum radiation from a population of compact, actively star-forming galaxies at redshift z ~ 0.2−0.3, also known as “green peas”. For the potential similarities with high-redshift galaxies and impact on the reionization of the universe, we study the green pea Lyα spectra, which are mostly double-peaked, unlike in any other galaxy sample. If the double peaks are a result of radiative transfer, they can be a useful source of information on the green pea interstellar medium and ionizing radiation escape. Methods. We select a sample of twelve archival green peas and we apply numerical radiative transfer models to reproduce the observed Lyα spectral profiles, using the geometry of expanding, homogeneous spherical shells. We use ancillary optical and ultraviolet data to constrain the model parameters, and we evaluate the match between the models and the observed Lyα spectra. As a second step, we allow all the fitting parameters to be free, and examine the agreement between the interstellar medium parameters derived from the models and those from ancillary data. Results. The peculiar green pea double-peaked Lyα line profiles are not correctly reproduced by the constrained shell models. Conversely, unconstrained models fit the spectra, but parameters derived from the best-fitting models are not in agreement with the ancillary data. In particular: 1) the best-fit systemic redshifts are larger by 10–250 km s−1 than those derived from optical emission lines; 2) the double-peaked Lyα profiles are best reproduced with low-velocity (≲150 km s−1) outflows that contradict the observed ultraviolet absorption lines of low-ionization-state elements with characteristic velocities as large as 300 km s−1; and 3) the models need to consider intrinsic Lyα profiles that are on average three times broader than the observed Balmer lines. Conclusions. Differences between the modelled and observed velocities are larger for targets with prominent Lyα blue peaks. The blue peak position and flux appear to be connected to low column densities of neutral hydrogen, leading to Lyα and Lyman-continuum escape. This is at odds with the kinematic origin of the blue peak in the homogeneous shell models. Additional modelling is needed to explore alternative geometries such as clumpy media and non-recombination Lyα sources to further constrain the role and significance of the Lyα double peaks.

Recovering the systemic redshift of galaxies from their Lyman alpha line profile

Abstract The Lyman alpha (Ly α) line of Hydrogen is a prominent feature in the spectra of star-forming galaxies, usually redshifted by a few hundreds of km s−1 compared to the systemic redshift. This large offset hampers follow-up surveys, galaxy pair statistics, and correlations with quasar absorption lines when only Ly α is available. We propose diagnostics that can be used to recover the systemic redshift directly from the properties of the Ly α line profile. We use spectroscopic observations of Ly α emitters for which a precise measurement of the systemic redshift is available. Our sample contains 13 sources detected between z ≈ 3 and z ≈ 6 as part of various multi-unit spectroscopic explorer guaranteed time observations. We also include a compilation of spectroscopic Ly α data from the literature spanning a wide redshift range (z ≈ 0–8). First, restricting our analysis to double-peaked Ly α spectra, we find a tight correlation between the velocity offset of the red peak with respect to the systemic redshift, $V_{\rm peak}^{\rm red}$, and the separation of the peaks. Secondly, we find a correlation between $V_{\rm peak}^{\rm red}$ and the full width at half-maximum of the Ly α line. Fitting formulas to estimate systemic redshifts of galaxies with an accuracy of ≤100 km s−1, when only the Ly α emission line is available, are given for the two methods.

An Empirical Model of the Variation of the Solar Lyman‐α Spectral Irradiance

AbstractWe propose a simple model that computes the spectral profile of the solar irradiance in the hydrogen Lyman alpha line, H Ly‐α (121.567 nm), from 1947 to present. Such a model is relevant for the study of many astronomical environments, from planetary atmospheres to interplanetary medium. This empirical model is based on the SOlar Heliospheric Observatory/Solar Ultraviolet Measurement of Emitted Radiation observations of the Ly‐α irradiance over solar cycle 23 and the Ly‐α disk‐integrated irradiance composite. The model reproduces the temporal variability of the spectral profile and matches the independent SOlar Radiation and Climate Experiment/SOLar‐STellar Irradiance Comparison Experiment spectral observations from 2003 to 2007 with an accuracy better than 10%.

Hysteresis Effect in the Activity Indices of the Atmospheres of the Sun and Solar-Type Stars During the Rising and Falling Phases of Cycles

The hysteresis effect that shows up as a nonunique relationship among the emissions from the photosphere, chromosphere, and corona during the rising and falling phases of solar and stellar activity is analyzed. The following solar indices are analyzed and compared in different phases of the cycle: the radiative flux in the hydrogen Lyman alpha line FLα, radio emission at 10.7 cm F10.7, the sunspot number SSN, the radiative flux in the 530.0 nm green coronal line F530.3, the solar constant TSI, and the relative flux ratio c/w (ratio of the fluxes in the center and in the wings) for the 280 nm Mg II line. In stars with cycles, a hysteresis effect is observed between the CaII chromospheric S-activity index for stars in the Mount Wilson HK project and the photospheric flux Fph for these stars.

THE Lyα REFERENCE SAMPLE. I. SURVEY OUTLINE AND FIRST RESULTS FOR MARKARIAN 259

The Lyman-alpha reference sample (LARS) is a program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the astrophysics of the visibility and strength of the Lyman-alpha (Lya) line of hydrogen. This article presents an overview of the survey, its selection function and HST imaging observations. The sample was selected from the GALEX+SDSS catalogue at z=0.028-0.19, in order to allow Lya to be captured with combinations of long pass filters in the Solar Blind Channel (SBC) of HST/ACS. In addition, LARS utilises Halpha and Hbeta narrow, and U, B, i broad-band imaging with ACS and WFC3. In order to study galaxies in which large numbers of Lya photons are produced we demanded an Halpha equivalent width > 100{\AA}. The sample of 14 galaxies covers far UV (FUV) luminosities that overlaps with those of high-z Lya emitters and Lyman Break Galaxies (LBGs). We present the reduction steps used to obtain the Lya images, including our LARS eXtraction software (LaXs) which utilises pixel-by-pixel spectral synthesis fitting to subtract the continuum at Lya. We demonstrate that the use of SBC long pass filters dramatically increase the signal to noise compared to the nominal Lya filter in SBC. To exemplify, we present results for Mrk 259. This irregular galaxy shows extended but strongly asymmetric Lya emission. Spectroscopy from HST/COS show a moderate outflow in the neutral ISM and an asymmetric Lya profile. Radiative transfer modeling is able to reproduce the Lya line profile, confirming the presence of an outflow. The integrated photometry provides a Lya luminosity of 1.3E42 erg/s an equivalent width W(Lya) =45{\AA} and a FUV absolute magnitude -19.2. Mrk 259 would hence be detectable in high-z Lya and LBG surveys. The total Lya escape fraction is 12%, similar to that observed at z>4. (shortened)

Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b

Atmospheric escape has been detected from the exoplanet HD 209458b through transit observations of the hydrogen Lyman-alpha line. Here we present spectrally resolved Lyman-alpha transit observations of the exoplanet HD 189733b at two different epochs. These HST/STIS observations show for the first time, that there are significant temporal variations in the physical conditions of an evaporating planetary atmosphere. While atmospheric hydrogen is not detected in the first epoch observations, it is observed at the second epoch, producing a transit absorption depth of 14.4+/-3.6% between velocities of -230 to -140 km/s. Contrary to HD 209458b, these high velocities cannot arise from radiation pressure alone and require an additional acceleration mechanism, such as interactions with stellar wind protons. The observed absorption can be explained by an atmospheric escape rate of neutral hydrogen atoms of about 10^9 g/s, a stellar wind with a velocity of 190 km/s and a temperature of ~10^5K. An X-ray flare from the active star seen with Swift/XRT 8 hours before the second-epoch observation supports the idea that the observed changes within the upper atmosphere of the planet can be caused by variations in the stellar wind properties, or by variations in the stellar energy input to the planetary escaping gas (or a mix of the two effects). These observations provide the first indication of interaction between the exoplanet's atmosphere and stellar variations.

An annular eclipse on May 31, 2003, observed in extreme ultraviolet

The CORONAS-F spacecraft crossed the zone of the ring solar eclipse three times on May 31, 2003. A considerable decrease in solar radiation was detected by the spacecraft instruments for these moments. The passages through the eclipse zone were registered by the VUSS instrument, which measured the shortwave solar radiation flux near the hydrogen Lyman alpha line, and by the DIFOS instrument, which was sensitive to infrared, visible, and near-ultraviolet radiation. The eclipse is also clearly seen in solar images obtained by the X-ray SPIRIT telescope. Some details of measurement results are discussed.

The Lyman-alpha glow of gas falling into the dark matter halo of a z = 3 galaxy.

Quasars are the visible signatures of gas falling into the deep potential well of super-massive black holes in the centres of distant galaxies. It has been suggested that quasars are formed when two massive galaxies collide and merge, leading to the prediction that quasars should be found in the centres of regions of largest overdensity in the early Universe. In dark matter (DM)-dominated models of the early Universe, massive DM halos are predicted to attract the surrounding gas, which falls towards their centres. The neutral gas is not detectable in emission by itself, but gas falling into the ionizing cone of such a quasar will glow in the Lyman-alpha line of hydrogen, effectively imaging the DM halo. Here we present a Lyalpha image of a DM halo at redshift z = 3, along with a two-dimensional spectrum of the gaseous halo. Our observations are best understood in the context of the standard model for DM haloes; we infer a mass of (2 - 7) x 10(12) solar masses (M(\circ)) for the halo.

A large population of 'Lyman-break' galaxies in a protocluster at redshift z approximately 4.1.

The most massive galaxies and the richest clusters are believed to have emerged from regions with the largest enhancements of mass density relative to the surrounding space. Distant radio galaxies may pinpoint the locations of the ancestors of rich clusters, because they are massive systems associated with 'overdensities' of galaxies that are bright in the Lyman-alpha line of hydrogen. A powerful technique for detecting high-redshift galaxies is to search for the characteristic 'Lyman break' feature in the galaxy colour, at wavelengths just shortwards of Lyalpha, which is due to absorption of radiation from the galaxy by the intervening intergalactic medium. Here we report multicolour imaging of the most distant candidate protocluster, TN J1338-1942 at a redshift z approximately 4.1. We find a large number of objects with the characteristic colours of galaxies at that redshift, and we show that this excess is concentrated around the targeted dominant radio galaxy. Our data therefore indicate that TN J1338-1942 is indeed the most distant cluster progenitor of a rich local cluster, and that galaxy clusters began forming when the Universe was only ten per cent of its present age.

真空紫外光‐イオントラップ／イオン化ＴＯＦＭＳによるごみ焼却炉排出ガス中のダイオキシン前駆体ＴＣＢのリアルタイム計測

Real-time measurement of the 1,2,4-trichlorobenzene (TCB) which is a precursor of dioxin was developed for discharge reduction of the dioxin in exhaust gas from an incinerator. The ion yield was improved using 1-photon ionization by vacuum ultraviolet (Lyman-alpha line of hydrogen (121.6nm)) and ion trap, after solid matters such as a dust were removed. Furthermore, TCB was quantitatively analyzed using the TCB fragment ion generated by ion collision in the ion trap. This method is possible to avoid the influence of much water in the exhaust gas. The calibration curve was described as Y = 0.052X + 4.2 (R2 = 0.9967), and the detection limit was approximately 80 ng/m3 N as S/N = 2. This calibration curve was sufficiently effective to practical exhaust gas of which TCB concentration is in the range between 0.0 and 6.0 μg/m3 N. It also presents the real-time monitoring of the 18 s intervals which is due to the signal output.

Sudden solar wind dynamic pressure enhancements and dayside detached auroras: IMAGE and DMSP observations

Dayside detached auroras (DDA) refer to auroras observed separate from the equatorward edge of the main oval on the dayside. They are studied here using IMAGE FUV and DMSP particle data. Occurrence of these DDA appears to be correlated with sudden solar wind dynamic pressure enhancements and northward interplanetary magnetic field, as monitored by the Wind satellite. They are usually very dynamic and short‐lived with a lifetime of the order of 10 minutes. Out of the three FUV instrument channels on IMAGE, DDA are best detected by the IMAGE FUV SI‐12 instrument, which measures intensities of the Doppler red‐shifted Hydrogen Lyman Alpha line. This indicates that energetic proton precipitation is the major component. Simultaneous DMSP particle observations confirm that energetic protons (>10 keV) in the dayside inner magnetosphere are the primary source of those DDA detected by the SI‐12 instrument. DMSP also detected significant electron fluxes associated with the DDA, but the electron precipitations have little or no contribution to the DDA intensities detected by the SI‐12 instrument. Precipitations of energetic protons (electrons) which caused DDA could be explained by enhanced cyclotron instability which arose from adiabatic compression following sudden solar wind dynamic pressure enhancements.

Determination of atomic hydrogen densities in gases by a deuterium based Lyman-alpha absorption method

We discuss the variant of a method for the determination of absolute hydrogen atom densities based on the absorption of the hydrogen Lyman-alpha line. Previously, we demonstrated that by using a simple vacuum ultraviolet spectrometer with low resolution an accuracy of better than 50% for the determined hydrogen atom densities can be obtained for transmissions ranging from 10% to 90%. For transmissions outside of this range excessive errors occur, thus, limiting the usefulness of the method to a certain range of hydrogen atom densities, depending on absorber length and temperature. This range of atomic hydrogen densities accessible to the measurement can be extended by the new method that consists of using well-defined mixtures of hydrogen and deuterium in the absorber. Using a source of either hydrogen or deuterium Lyman-alpha radiation, only one sort of atoms contributes to the absorption. Thus, by selecting an appropriate mixture of hydrogen and deuterium, the range of atom densities accessible to the measurement can be extended to higher densities. Using well-defined mixtures ranging from 1% hydrogen in deuterium to 2% deuterium in hydrogen as absorbers, we were able to determine hydrogen atom densities up to a factor 100 higher than those measured previously in pure hydrogen. Using mixtures down to the natural abundance of deuterium in hydrogen, the measurement of even higher atom densities seems possible. The effect of the difference of the energies of dissociation of hydrogen and deuterium has been investigated using a computer model of relevant chemical processes. In most situations, this effect is smaller than the experimental error. The main limitation of the method is its sensitivity to absorption by impurities, as many molecular gases absorb Lyman-alpha radiation.

An extreme ultraviolet radiation source for the simulation of the ionosphere

An extreme ultraviolet (EUV) radiation source for space simulation of plasma and other related phenomena in the laboratory has been developed. A total of forty-eight small EUV lamps are put together to give a radiation diameter of more than 30 cm. The intensity of this lamp at the hydrogen Lyman-alpha line is more than twenty five times stronger than sunlight at the same wavelength and at a distance of about 30 cm from the source. The source is capable of emitting EUV radiations from 110 nm to the longer wavelengths, either continuously or in pulses, and has been used to produce a plasma of 105 els/cm3 when the pressure of NO gas in the chamber was 10−4 Torr. Since this plasma is extremely calm and fairly Maxwellian, it can be used to study the electron collection mechanism of a probe in a collision dominant medium. The source was also utilized to study the interaction between vibrationally excited nitrogen molecules and thermal electrons.

UV observations of the extended corona

Abstract Measurements of the intensities and profiles of the resonantly scattered hydrogen Lyman-alpha line at 1216 A have provided important insights on the physical conditions in the extended corona where the solar wind originates. Comparisons of measured kinetic temperatures with predictions of models suggest that there is proton heating and/or a nonthermal contribution to the motions of coronal protons between 1.5 and 4 solar radii. Comparisons of measured Lyman-alpha intensities with predictions of models provide evidence for subsonic flow for r ⊙ in a quiet region of the corona and two polar coronal holes observed near solar maximum. There is evidence for supersonic flow ( ∼ 200 km s −1 ) at r ≈ 2 R ⊙ in a large polar coronal hole observed in 1982. Future measurements of HI Lyman alpha and other coronal lines will greatly expand the quality and quantity of UV spectroscopic measurements of the extended corona.

Equivalent widths of hydrogen Lyman alpha line in an expanding spherical atmosphere

We have calculated the profiles of hydrogen Lyman a line in an expanding spherical atmosphere containing dust and gas. We have investigated the variation of equivalent widths with velocities of expansion of the atmosphere, together with the amount of dust present in the medium. We have drawn curves of growth for different velocities and dust optical depths